If this feature is added I would suggest that the other way around should also be done. Meaning: Map -> Bean , Set -> Bean

java.util.Map<String, String> myMap(); with entry {"last_name","some name"}

public class Bean{

String firstName;
String lastName;

// getters + setters
}

@Mapper
public interface Mapper{

@Mapping(source="last_name", target="lastName")
public Bean maptoBean (java.util.Map<String,String> myMap)

}

additionally would be very usefull to use for HttpServletRequest e.g. Map<String, String[]> parameters = request.getParameterMap();
or other combinations like Map<String, List<String>>, ...

I am looking for something similar (if not the same)

1. Mapping bean property to target map with given key name
2. Mapping target map with given key name to bean property

for example

public class ClassA {
Map<String, String> properties;
}

public class ClassB {
String serverName;
}

@mapping(target="properties(key='server name')", source="serverName")
public ClassA b2a (ClassB b);

@mapping(target="serverName", source="properties(key='server name'")
public ClassB a2b (ClassA a);

Similar functionality is available in Dozer: http://dozer.sourceforge.net/documentation/mapbackedproperty.html
It would be great to have it in MapStruct

actually we are using dozer now. but its performance is not good. we are considering to move to either mapstruct or other tools.

I would like to see this feature in MapStruct as well, if possible.

People are supposed to be using https://github.com/FasterXML/jackson for that purpose. Never tested it!
It would be great to have MapStruct builtin feature.

Instead of target use (new) key (by default String)- something like:

@Mapper
public interface Mapper{

@Mapping(key="key1", source="bar")
@Mapping(key="key2", source="i") // Boxing 
@Mapping(key="key3", expression="java(obj.toString())")
public java.util.Map<String,String> beanToMap(Foo foo);

}

where Foo is

class Foo {
    String bar;
    int i;
    Object obj;
}

Ignore duplicated keys / add flag duplicates to not ignore:

@Mapper(duplicates = MapKeysDuplicatedStrategy.ERROR)